Kavli Affiliate: E. P. S. Shellard

| First 5 Authors: Amelia Drew, E. P. S. Shellard, , ,

| Summary:

We implement adaptive mesh refinement (AMR) simulations of global topological

strings using the public numerical relativity code, GRChombo. We perform a

quantitative investigation of the dynamics of single sinusoidally displaced

string configurations, studying a wide range of string energy densities $mu

propto ln{lambda}$, defined by the string width parameter $lambda$ over two

orders of magnitude. We investigate the resulting massless (Goldstone boson or

axion) radiation signals, using quantitative diagnostic tools to determine the

eigenmode decomposition. Given analytic radiation predictions, we compare the

oscillating string trajectory with a backreaction model accounting for

radiation energy losses, finding excellent agreement. We establish that

backreaction decay is accurately characterised by the inverse square of the

amplitude being proportional to the inverse tension $mu$ for $3lesssim

lambda lesssim 100$. We conclude that analytic radiation modelling in the

thin-string (Nambu-Goto) limit provides the appropriate cosmological limit for

global strings. We comment on the implications of this study for predictions of

axions and gravitational waves produced by cosmic string networks.

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